1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for determining a trigger condition for client cooperation in a wireless communication system.
2. Related Art
With the advent of a ubiquitous environment, there is a rapid increase in a demand for receiving a seamless service anytime anywhere by using equipments. In order to satisfy such a demand, a client cooperation technique may be introduced in a wireless communication system. The client cooperation technique refers to a technique by which a specific device helps transmission of another device. That is, one device may directly communicate with a base station (BS) or may indirectly communication with the BS by the aid of another device. A source device refers to a device which communicates with the BS through a connection with another device. A cooperation device refers to a relay entity which helps the source device to communicate with the BS.
The client cooperation technique has an effect of lower power consumption. In terms of a device, a path-loss can be decreased by the client cooperation technique, thereby being able to decrease transmit power. In terms of a network, total network power consumption can be decreased. In addition, the client cooperation technique has an effect of throughput enhancement. In terms of a device, a source device can use a good-quality link between a cooperation device and a BS and between BSs. In addition, an antenna extension gain can be obtained. In terms of the network, network capacity can be increased by using client clustering based on frequency reuse without an additional infrastructure.
The client cooperation technique can be more effectively used in a multi-radio access technology (RAT) device. The multi-RAT device refers to a device that can operate in a plurality of communication systems. For example, the multi-RAT device can operate both in institute of electrical and electronics engineers (IEEE) 802.16m and IEEE 802.11. To provide an easiness access to the BS anytime anywhere and to maintain effective performance, the multi-RAT device can use a multi-RAT client cooperation technique (i.e., improved tethering) in a heterogeneous network.
In order for a certain device which is under communication by being directly connected to a BS to perform communicate by being indirectly connected to the BS according to client cooperation by the aid of another device, a special trigger is required for communicating with the BS according to the client cooperation. That is, a special trigger condition must be satisfied to perform the client cooperation.
Accordingly, there is a need for a method of determining a trigger condition for client cooperation and an operation between a BS and a device when the trigger condition is satisfied.